European Patent Application 244 303 discloses a screw and nut device that is subject to alternate axial forces in two directions. The thread of the screw has determined helix and pressure angles that are selected so that the screw can cause a translation and a rotation in the nut under an axial thrust exerted in a first direction (termed reversible) by a spring, and so that the screw cannot cause either a translation or a rotation in the nut when subjected to axial thrust in a second direction opposite to the first direction (termed irreversible) by the spring. The assembly can compensate for automatic play in systems subject to alternate longitudinal forces, such as electric motor shafts or cable controls.
A disadvantage of this system is that under certain conditions, such as when moisture or grease are present, the device is no longer irreversible. When the screw undergoes the axial thrust in the second direction from the spring, the screw causes an undesirable translation and rotation in the nut. The assembly that compensates for play therefore becomes ineffective.
There is therefore a need for a play compensation device that is effective under all conditions.